The importance of luteinizing hormone in the control of inhibin and progesterone secretion by the human corpus luteum

Abstract:

Serum inhibin levels rise markedly during the luteal phase of the human
menstrual cycle and are closely correlated with serum progesterone (P)
levels, suggesting that the corpus luteum (CL) secretes inhibin. While FSH
is the major regulator of inhibin secretion by the granulosa cells, the
control of CL inhibin secretion is unclear. We hypothesized that, like P,
CL inhibin secretion would be LH dependent. To examine this possibility,
normal women were given the GnRH antagonist [Ac-D2Nal1, D4CL Phe2, D3Pal3,
Arg5, DGlu6 (AA), DAla10]GnRH (Nal-Glu antagonist) for 3 consecutive days
commencing on day 6-8 of the luteal phase. The daily doses were 2.5 (n =
3), 10 (n = 4), and 25 micrograms/kg (n = 5), sc. Serum LH levels fell 2 h
after injection, and the fall was maximal (70-74%) at 6 h; the degree of
suppression was not dose dependent. The duration of suppression was dose
related, being less than 12 h, between 12, and 24 h, and more than 24 h
for the 2.5, 10, and 25 micrograms/kg doses, respectively. Serum FSH
levels declined by 22-43%, but the effect was not dose related. Serum P
levels fell by 42-45% 8 h after each dose of antagonist. They returned to
baseline 24 h after the 2.5 micrograms/kg dose, but after both the 10 and
25 micrograms/kg doses serum P levels continued to fall, and menstrual
bleeding commenced within 48-72 h after the first antagonist injection.
Serum inhibin levels were not altered relative to normal cycles by the 2.5
micrograms/kg dose, but fell by 48% and 58%, and 62% and 73% respectively,
48 and 72 h after the 10 and 25 micrograms/kg doses, respectively. Serum P
and inhibin levels correlated closely in all women. To examine the
relative roles of FSH and LH in the control of CL function, Nal-Glu
antagonist (25 micrograms/kg, sc) was administered at 0 and 24 h
commencing on day 6-8 of the luteal phase, in combination with either
human menopausal gonadotropin (hMG; 150 IU, im, every 12 h) or hCG (1500
IU, im, once), both commencing at 0 h. hMG administration led to a rapid
(by 2 h) and marked (3- to 9-fold) rise in serum FSH levels, whereas serum
LH remained low, similar to antagonist alone treatment cycless.(ABSTRACT
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